There exists a disease condition in the leg veins called venous synechiae or septae, also called trabeculated or fenestrated veins. All of the foregoing terms refer to flow-obstructing structures present in human veins which are thought to be residual intraluminal scar tissue resulting from long-term presence of fibrotic thrombus. After thrombolysis, either through natural lysis or treatment via thrombolytics or thrombectomy, fibrous structures often remain. This partial obstruction of flow leads to clinical conditions such as hypertension, edema, chronic pain, and non-healing ulcers. The condition is also a risk for further thrombosis, and can also prevent or interfere with interventions such as balloon angioplasty or stenting.
Venous synechiae restrict blood flow via two mechanisms: (1) reduction of the effective luminal cross-sectional area due to their physical presence, and (2) reduction of the overall venous luminal diameter caused by stored tension in the synechiae that pulls the vessel walls inward. Puggioni et al carried out endophlebectomies, or removal of venous synechiae, on 13 patients in an open surgical fashion. In this experience, Puggioni describes the second, more subtle obstructive impact of venous synechiae: “After removal of the synechiae, an increase in luminal diameter is observed as a result of the release of constricting bands, and this contributes to improved vessel compliance.” Puggioni et al. Surgical disobliteration of postthrombotic deep veins—endophlebectomy—is feasible. J Vasc Surg 2004; 39:1048-52.
While complete removal of venous synechiae may be ideal for maximizing restoration of flow to a venous lumen, there is a clinical benefit to relieving the tension imposed on the vessel wall by cutting the synechiae. Cutting the synechiae also enables intraluminal delivery of a balloon catheter or stent delivery system which can then be deployed to expand the vessel (via dilation or stenting).
Individual synechiae are often tough and fibrous in nature, and can also be quite dense in the vessel lumen. Current methods for treating or otherwise reducing the physiological impact of the synechiae include the use of cutting balloons, balloon angioplasty, or stenting to cut through the fibrous synechiae structures. However, such methods have proven to have limited efficacy on restoring flow due to the toughness and/or density of the obstructions. Direct surgical excision of the synechiae have also been attempted but open vascular surgical procedures can themselves lead to post-surgical complications such as hematoma, infection, thrombosis, or restenosis. Furthermore, a direct surgical approach cannot easily treat long lengths of veins or multiple sites in one patient without causing increased trauma to the patient.
One existing approach for cutting intraluminal fibers involves a device with a grasping component and a tubular member with internal cutting devices. In this approach, the grasper pulls fibers into the tubular member where they are severed on contact with the cutting devices. However, the design of such a device has limited ability to cut across the entire diameter of a vessel, or to cut through the bulk of fibrous material often seen in the veins. Other cutting catheter technology exists, such as cutting balloons, atherectomy devices, chronic total occlusion catheter, or embolectomy catheters. However, none of these devices were designed for cutting fibrous and bulky intravascular structures, and are therefore limited in their ability to treat these conditions. Devices such as valvulotomes are designed to remove existing valves from veins, for example in procedures utilizing veins in connection with in situ bypass graft placement or treating AV fistulas. However, vein valves are relatively thin structures and valvulotome devices are not designed to cut particularly tough tissue. As such, valvutome devices would be unsuitable for cutting tissue structures such as venous synechiae. Also, these technologies require the user to pull the device past the tissue in order to cut, thus applying a shear force on the vessel wall and surrounding tissue. If there is any resistance to cutting, the applied force may result in considerable pain to the patient. Even in cases requiring minimal force, the act of cutting will result in losing access across the treatment site and requiring re-accessing the site if the cuts were unsuccessful or inadequate on the initial pass.